Various downhole well configurations, including vertical, directional, or horizontal, are used in oil and gas production from subterranean formations. With reference to FIG. 1, horizontal wells W typically comprise a relatively vertical section V (which may be vertical or off-vertical) and a relatively lateral section L (which may or may not be horizontal) that are connected by a curved ‘build’ section, often referred to as the ‘heel’ H. In almost all cases, the lateral section L is the productive target of the well W and will be configured to allow the inflow of fluids (oil/water/gas) from the reservoir into the wellbore.
Unfortunately, due to the configuration of horizontal wells, debris D can accumulate along the horizontal or deviated section of the well, clogging the annulus and impacting bottomhole pressure. Such debris, which can include residual drilling mud and/or cuttings, frac sand from post-frac stimulation treatments, produced formations sand, etc., can also damage downhole equipment. Over time, the built-up debris can significantly obstruct the wellbore, reducing production and requiring that the wellbore debris be removed or “cleaned” therefrom.
Various wellbore cleanout systems and methods have been developed for removing sand and other wellbore debris from horizontal wells. Mechanical tools for miling and scraping, hydraulic tools for getting and flow back, and chemical systems used to dissolve the debris or increasing fluid carrying capacities are known. To date, however, such systems have difficulty accessing debris forming beds underneath or uphole of the equipment, particularly with the development of longer horizontal sections (e.g. deeper wells). Such systems also have difficulty generating and maintaining sufficient fluid velocities to lift and carry the sand and debris along the wellbore and up to the surface, necessitating the use of large, complicated equipment, or the isolation of smaller section of bore to be cleaned.
Further, many systems often underperform due to lost circulation or poor circulation velocities, potentially causing fluid losses into the reservoir and significantly increasing operation costs. Systems can also be limited to the constraints of the reservoir, particularly where transport velocities and pick-up of the debris is restricted to the rate at which the reservoir can supply fluid to the wellbore. The resulting inflow rate is often insufficient to flush the sand, impairing the overall cleaning performance.
There is a need for a wellbore cleanout system that overcomes the above-noted problems.